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A095385 Numbers n with property that n is a peak value in 3x+1 trajectory such that both n+1 and n-1 are prime numbers. 0
4, 72, 180, 192, 228, 240, 312, 600, 1092, 1152, 1428, 1488, 1608, 1620, 1872, 2088, 2112, 2592, 2688, 3000, 3168, 3252, 3360, 3528, 4272, 4548, 4800, 5640, 6552, 6960, 7488, 7560, 8088, 8292, 8388, 8820, 9000, 9012, 9240, 9768, 10008, 10068, 10272 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

In such cases it seems that initial value equals peak value. Proof needed!

LINKS

Table of n, a(n) for n=1..43.

EXAMPLE

n=72: list={72,36,18,9,28,14,7,22,11,34,17,52,26,13,40,20,10,5,16,8,4,2,1}

MATHEMATICA

c[x_]:=c[x]=(1-Mod[x, 2])*(x/2)+Mod[x, 2]*(3*x+1); c[1]=1; fpl[x_]:=FixedPointList[c, x]; {$RecursionLimit=1000; m=0}; Do[If[PrimeQ[1+Max[fpl[n]]&&PrimeQ[ -1+Max[fpl[n]]], Print[n]], {n, 1, 10000}]

CROSSREFS

Cf. A025586.

Sequence in context: A113839 A077112 A203537 * A071683 A192826 A190398

Adjacent sequences:  A095382 A095383 A095384 * A095386 A095387 A095388

KEYWORD

nonn

AUTHOR

Labos Elemer, Jun 14 2004

STATUS

approved

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Last modified October 17 21:57 EDT 2019. Contains 328134 sequences. (Running on oeis4.)